1. Field of the Invention
The present invention relates to a light-emitting diode which comprises III-V semiconductor material having a pn junction as its light-active zone from which luminescent radiation having a pressure-dependent nature is emitted.
2. Description of the Prior Art
It is well known in the art that, given influence of mechanical pressure on a light-emitting diode, the band gap of the semiconductor material of the diode is changed and, therefore, a pressure-dependent frequency change of the emitted luminescent radiation occurs. The use of such light-emitting diodes as pressure sensors is basically opposed by the disadvantage that frequency shifts of emitted radiation can be quantitatively detected as would be required for a measuring sensor only with very complex structure.
U.S. Pat. No. 3,387,230 discloses an electro-optical transistor wherein one region (of the semiconductor body) of the transistor is exposed to selective, elastic mechanical distortion. Therefore, influence on the photons traversing this region is also achieved, as indicated at column 2, lines 31-34. Therefore, a region in the semiconductor body which is located adjacent to the pn junction generating the radiation is exposed to elastic distortion. Therefore, the generation of radiation is not influenced as a result of mechanical effect (column 2, line 55 through column 3, line 3). The physical foundation of the subject matter of this patent is that different absorption of the radiation already generated is present, being influenced by mechanical distortion and being frequency-dependent (column 6, lines 49-62).
British Letters Pat. No. 1,028,250 discloses a semiconductor device with which existing mechanical oscillations are to be converted into electrical signals. The semiconductor devices in this case is a laser diode which differs from a light-emitting diode in that it is an optical amplifier and its semiconductor body is necessarily designed as an optical resonator having mutually-opposed reflection surfaces. Given this structure, the generation of radiation is not influenced by the mechanical oscillations. On the contrary, what is exploited is that a movement of the overall radiation-generating diode effected by mechanical oscillation makes the transmission of its radiation to a stationary receiver diode dependent on such motion. This, for example, could not be achieved with a light-emitting diode instead of the laser diode since a light-emitting diode does not exhibit focused radiation conversion as occurs given a laser diode and the light-emitting diode would permit radiation to proceed into the receiver practically uninfluenced by its mechanical motion.
Disclosed in "Applied Physics Letters", Vol. 29 (1969), pp. 615-617, is a light-emitting diode which is modulated with hydrostatic pressure, the light-emitting diode being a nitrogen-doped gallium arsenide phosphide diode. The material composition of the diode in this case is necessarily of such nature that the radiation-generating charge carrier transitions are not direct transitions from the conduction band to the valence band, but are necessarily indirect transitions over nitrogen luminous centers. Given such a diode, a certain pressure dependency of the radiation generation can be identified from which scientific perceptions concerning the physical mechanism of the radiation generation with charge carrier junctions via nitrogen luminous centers can be obtained. As specified in this publication at Page 616, left-hand column, center, an intensity decrease of approximately 85% was identified; however, for a pressure change from zero to the enormous value of 6 Kbar, i.e. approximately 6 tons/cm.sup.2.
A further publication, namely the German published patent application No. 31 01 047 discloses a fiber-optical measuring device for measuring a force or a pressure. The concern given this measuring device is to make the measuring signal independent of changes of both the intensity and the wavelength of the light of the appertaining light source. The measuring device is designed such that the optical signal received in the detector system is dependent on the pressure or, respectively, on the force to be measured. The light-emitting diode of this measuring device, generating primary radiation, is not subjected to any mechanical pressure. On the contrary, the mechanical pressure (F) influences an additional semiconductor sensor which, as a result of incident light radiation from the light-emitting diode, emits a pressure-dependent luminescent spectrum. As indicated in this publication, the pressure or, respectively, force influence on the sensor is to such effect that the frequency of the luminescent radiation of the sensor is changed. This pressure-dependent frequency change is then determined in the detector upon the use of a further, frequency-selective filter. The sensor influenced by the pressure or, force, moreover, has no electrical terminals, i.e. it is not permeated by current.